We investigate the three-dimensional （3D） scattering problem of an incident plane shear horizontal wave by a partly through-thickness hole in an isotropic plate, in which the Lamb wave modes are also included due to...We investigate the three-dimensional （3D） scattering problem of an incident plane shear horizontal wave by a partly through-thickness hole in an isotropic plate, in which the Lamb wave modes are also included due to the mode conversions by the scattering obstacle in the 3D problem. An analytical model is presented such that the wave fields are expanded in all of propagating and evanescent SH modes and Lamb modes, and the scattered far-fields of three fundamental guided wave modes are analyzed numerically for different sizes of the holes and frequencies. The numerical results are verified by comparing with those obtained by using the approximate Poisson/Mindlin plate model for small hole radius and low frequency. It is also found that the scattering patterns are different from those of the SO wave incidence. Our work is useful for quantitative evaluation of the plate-like structure by ultrasonic guided waves.展开更多
We present a theoretical investigation of the scattering of high frequency S0 Lamb mode from a circular blind hole defect in a plate based on the 3D theory. The SO wave is incident at the frequency above the A1 mode c...We present a theoretical investigation of the scattering of high frequency S0 Lamb mode from a circular blind hole defect in a plate based on the 3D theory. The SO wave is incident at the frequency above the A1 mode cut-off frequency, in which the popular approximate plate theories are inapplicable. Due to the non-symmetric blind hole defect, the scattered fields will contain higher order converted modes in addition to the fundamental SO and AO modes. The far-field scattering amplitudes of various propagating Lamb modes for different hole sizes are inspected. The results are compared with those of lower frequencies and some different phenomena are found. Two-dimensional Fourier transform （2DFT） results of transient scattered Lamb and SH wave signals agree well with the analytical dispersion curves, which check the validity of the solutions from another point of view.展开更多
Lamellar tearing and crack-induced brittle failures along steel plates in the through-thickness direction seriously threaten the safety and reliability of steel thick plate structures in construction and service, espe...Lamellar tearing and crack-induced brittle failures along steel plates in the through-thickness direction seriously threaten the safety and reliability of steel thick plate structures in construction and service, especially at low ambient temperatures. Three kinds of tests, including uniaxial tensile tests, Charpy V-Notch impact tests, and three-point bending （TPB） tests were performed at normal and low temperatures to investigate the through-thickness mechanical properties, impact and fraclure toughness of Q345B structural steel plates with thicknesses from 60 to 165 mm. The test specimens were mainly sampled along the through-thickness direction of the plate, but transverse specimens along the rolling direction were also involved. The ductility index （percentage reduction of area）, impact toughness index （Charpy impact energy）, and fracture toughness index （critical crack tip opening displacement （CTOD） values） all decrease as the temperature declines. All the mechanical properties and the impact and fracture toughness along the through-thickness direction are worse than those along the rolling direction. The results also offer experimental support for the determination of an evaluation indicator for structural steel thick plates with through-thickness characteristics.展开更多
Through-thickness heterogeneity in creep properties of 7B50-T7451 aluminum alloy Friction Stir Welding(FSW)joints was investigated.Creep tests for three slices of the FSW joint were conducted at the temperature of 150...Through-thickness heterogeneity in creep properties of 7B50-T7451 aluminum alloy Friction Stir Welding(FSW)joints was investigated.Creep tests for three slices of the FSW joint were conducted at the temperature of 150-200℃ and applied stress of 60-225 MPa.The theta projection method was used to predict creep curves and minimum creep rate.The results show that the minimum creep rate increases and creep rupture life decreases with the increase of creep temperature and applied stress.Creep properties of the FSW joint deteriorate along the thickness direction from the top to the bottom.The threshold stress of all three slices of the FSW joint decreases with the increase of creep temperature and even disappears at 200℃ for the bottom slice.Creep activation energy approaches the activation energy of the lattice self-diffusion of aluminum.The value of true stress exponent for different slices is approximately equal to three.The predominant creep mechanism of the FSW joint is dislocation viscous glide by lattice self-diffusion.What is more,a constitutive model is established based on the theta method to accurately describe creep behavior ofdifferent slices of the FSW joint.展开更多
Marciniack–Kuczinski(M–K)model is widely used to predict material's forming limit curve(FLC).The prediction of FLC traditionally neglected through-thickness normal stress.However,it cannot be neglected in some f...Marciniack–Kuczinski(M–K)model is widely used to predict material's forming limit curve(FLC).The prediction of FLC traditionally neglected through-thickness normal stress.However,it cannot be neglected in some forming processes.Much work has been done to study the effect of through-thickness normal stress on FLC with constant through-thickness normal stress or constant ratio of through-thickness normal stress and maximum principal stress.In addition,based on Nakazima test process,the ratio of through-thickness normal stress and maximum principal stress has been derived,which was a function of instantaneous thickness and loading path.Here,initial groove angle in M–K model was not considered.In this paper,uniaxial tension tests and Nakazima tests were performed on 7B04 aluminum alloy.Based on Hill 48 yield criterion and M–K model,the prediction model of FLC was established.The increase of thickness can enhance FLC.Meanwhile,it is necessary to consider through-thickness normal stress and initial groove angle in prediction model.On the left side of FLC,the effect of initial groove angle on FLC is weakened by increasing sheet thickness.On the right side of FLC,the effect of initial groove angle on FLC is strengthened by increasing sheet thickness.On the right side of FLC,the relation between limit strain points with different thicknesses is linear under one certain loading path.Thickness has decisive effect on through-thickness normal stress level and the changing trendy of through-thickness normal stress during calculation is different under different stress condition.展开更多
A modified MK model combined with ductile fracture criterion（DFC-MK model） is proposed to compute the forming limit diagrams（FLDs） of 5A06-O aluminum alloy sheet at different temperatures.The material constant（C...A modified MK model combined with ductile fracture criterion（DFC-MK model） is proposed to compute the forming limit diagrams（FLDs） of 5A06-O aluminum alloy sheet at different temperatures.The material constant（C） of ductile fracture criterion and initial thickness imperfection parameter（f0） at various temperatures are determined by using a new computing method based on wide sheet bending test.The FLDs at 20 and 200 °C are calculated through the DFC-MK model.The DFC-MK model,which includes the influence of through-thickness normal stress,is written into the subroutine VUMAT embedded in Abaqus/ Explicit.The cylindrical cup hydroforming tests are carried out to verify the model.The results show that compared with experimental observations,the predicted FLDs based on DFC-MK model are more accurate than the conventional MK model;the errors between the simulations and experiments in warm hydroforming are 8.23% at 20 °C and 9.24% at 200 °C,which verify the effectiveness of the proposed model.展开更多
Tubular members have been used for constructing offshore structures. Large-scale fatigue tests of welded tubular K-joints under the balanced in-plane bending brace were carried out to investigate the fatigue behavior ...Tubular members have been used for constructing offshore structures. Large-scale fatigue tests of welded tubular K-joints under the balanced in-plane bending brace were carried out to investigate the fatigue behavior of API 2W Gr.50 steel produced by POSCO. The experimental results were verified by numerical approaches and compared with the IIW, DnV RP-C203 and API RP 2A-WSD design curves. The test results based on the hot spot stress were in agreement with the design curves. The SCF factor for tubular K-joint was also obtained. The numerical parametric study of the K-joint (using the finite element program) was described and its results were compared with experimental results. The stress effects of various parameters including α, β, γ, τ and θ on the stress in the K-joint were investigated. The stress distribution for each parameter was introduced. The study showed that the maximum stress of the joint varied according to the variation of joint parameters.展开更多
To obtain the influence of fluid pressure and temperature on warm hydroforming of 5A06-O aluminum alloy sheet, the unified mechanics equilibrium equations, which take through- thickness normal stress and friction into...To obtain the influence of fluid pressure and temperature on warm hydroforming of 5A06-O aluminum alloy sheet, the unified mechanics equilibrium equations, which take through- thickness normal stress and friction into account, were established in spherical coordinate system. The distribution of through-thickness normal stress in the thickness direction was determined. The relation between through-thickness normal stress and fluid pressure was also analyzed in different regions of cylindrical cup. Based on the method of subtracting one increasing function from another, the constitutive equation of 5A06-O applied to warm hydroforming was established and in a good agreement with uniaxial tensile data. Based on whether the thickness variation was taken into account, two mechanic models were established to do the comparative study. The results for the studied case show that the calculated stress values are pretty close according to the two models and consistent with results of finite element analysis; the thickness distribution in flange computed by the second model conforms to the experimental data. Finally, the influences of fluid pressure on the flange thickness and radial stress were analyzed.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 11474195,11274226,51478258 and 51405287
文摘We investigate the three-dimensional （3D） scattering problem of an incident plane shear horizontal wave by a partly through-thickness hole in an isotropic plate, in which the Lamb wave modes are also included due to the mode conversions by the scattering obstacle in the 3D problem. An analytical model is presented such that the wave fields are expanded in all of propagating and evanescent SH modes and Lamb modes, and the scattered far-fields of three fundamental guided wave modes are analyzed numerically for different sizes of the holes and frequencies. The numerical results are verified by comparing with those obtained by using the approximate Poisson/Mindlin plate model for small hole radius and low frequency. It is also found that the scattering patterns are different from those of the SO wave incidence. Our work is useful for quantitative evaluation of the plate-like structure by ultrasonic guided waves.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11474195,11274226 and 61171145
文摘We present a theoretical investigation of the scattering of high frequency S0 Lamb mode from a circular blind hole defect in a plate based on the 3D theory. The SO wave is incident at the frequency above the A1 mode cut-off frequency, in which the popular approximate plate theories are inapplicable. Due to the non-symmetric blind hole defect, the scattered fields will contain higher order converted modes in addition to the fundamental SO and AO modes. The far-field scattering amplitudes of various propagating Lamb modes for different hole sizes are inspected. The results are compared with those of lower frequencies and some different phenomena are found. Two-dimensional Fourier transform （2DFT） results of transient scattered Lamb and SH wave signals agree well with the analytical dispersion curves, which check the validity of the solutions from another point of view.
基金the National Natural Science Foundation of China，the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘Lamellar tearing and crack-induced brittle failures along steel plates in the through-thickness direction seriously threaten the safety and reliability of steel thick plate structures in construction and service, especially at low ambient temperatures. Three kinds of tests, including uniaxial tensile tests, Charpy V-Notch impact tests, and three-point bending （TPB） tests were performed at normal and low temperatures to investigate the through-thickness mechanical properties, impact and fraclure toughness of Q345B structural steel plates with thicknesses from 60 to 165 mm. The test specimens were mainly sampled along the through-thickness direction of the plate, but transverse specimens along the rolling direction were also involved. The ductility index （percentage reduction of area）, impact toughness index （Charpy impact energy）, and fracture toughness index （critical crack tip opening displacement （CTOD） values） all decrease as the temperature declines. All the mechanical properties and the impact and fracture toughness along the through-thickness direction are worse than those along the rolling direction. The results also offer experimental support for the determination of an evaluation indicator for structural steel thick plates with through-thickness characteristics.
基金financially supported by the National Natural Science Foundation of China(No.52075450)the Fundamental Research Funds for the Central Universities,China(No.D5000220503).
文摘Through-thickness heterogeneity in creep properties of 7B50-T7451 aluminum alloy Friction Stir Welding(FSW)joints was investigated.Creep tests for three slices of the FSW joint were conducted at the temperature of 150-200℃ and applied stress of 60-225 MPa.The theta projection method was used to predict creep curves and minimum creep rate.The results show that the minimum creep rate increases and creep rupture life decreases with the increase of creep temperature and applied stress.Creep properties of the FSW joint deteriorate along the thickness direction from the top to the bottom.The threshold stress of all three slices of the FSW joint decreases with the increase of creep temperature and even disappears at 200℃ for the bottom slice.Creep activation energy approaches the activation energy of the lattice self-diffusion of aluminum.The value of true stress exponent for different slices is approximately equal to three.The predominant creep mechanism of the FSW joint is dislocation viscous glide by lattice self-diffusion.What is more,a constitutive model is established based on the theta method to accurately describe creep behavior ofdifferent slices of the FSW joint.
基金the support from the National Natural Science Foundation of China(51575028)the Fundamental Research Funds for the Central Universities(YWF-18-BJ-J-75)。
文摘Marciniack–Kuczinski(M–K)model is widely used to predict material's forming limit curve(FLC).The prediction of FLC traditionally neglected through-thickness normal stress.However,it cannot be neglected in some forming processes.Much work has been done to study the effect of through-thickness normal stress on FLC with constant through-thickness normal stress or constant ratio of through-thickness normal stress and maximum principal stress.In addition,based on Nakazima test process,the ratio of through-thickness normal stress and maximum principal stress has been derived,which was a function of instantaneous thickness and loading path.Here,initial groove angle in M–K model was not considered.In this paper,uniaxial tension tests and Nakazima tests were performed on 7B04 aluminum alloy.Based on Hill 48 yield criterion and M–K model,the prediction model of FLC was established.The increase of thickness can enhance FLC.Meanwhile,it is necessary to consider through-thickness normal stress and initial groove angle in prediction model.On the left side of FLC,the effect of initial groove angle on FLC is weakened by increasing sheet thickness.On the right side of FLC,the effect of initial groove angle on FLC is strengthened by increasing sheet thickness.On the right side of FLC,the relation between limit strain points with different thicknesses is linear under one certain loading path.Thickness has decisive effect on through-thickness normal stress level and the changing trendy of through-thickness normal stress during calculation is different under different stress condition.
基金Project(51175024)supported by the National Natural Science Foundation of China
文摘A modified MK model combined with ductile fracture criterion（DFC-MK model） is proposed to compute the forming limit diagrams（FLDs） of 5A06-O aluminum alloy sheet at different temperatures.The material constant（C） of ductile fracture criterion and initial thickness imperfection parameter（f0） at various temperatures are determined by using a new computing method based on wide sheet bending test.The FLDs at 20 and 200 °C are calculated through the DFC-MK model.The DFC-MK model,which includes the influence of through-thickness normal stress,is written into the subroutine VUMAT embedded in Abaqus/ Explicit.The cylindrical cup hydroforming tests are carried out to verify the model.The results show that compared with experimental observations,the predicted FLDs based on DFC-MK model are more accurate than the conventional MK model;the errors between the simulations and experiments in warm hydroforming are 8.23% at 20 °C and 9.24% at 200 °C,which verify the effectiveness of the proposed model.
文摘Tubular members have been used for constructing offshore structures. Large-scale fatigue tests of welded tubular K-joints under the balanced in-plane bending brace were carried out to investigate the fatigue behavior of API 2W Gr.50 steel produced by POSCO. The experimental results were verified by numerical approaches and compared with the IIW, DnV RP-C203 and API RP 2A-WSD design curves. The test results based on the hot spot stress were in agreement with the design curves. The SCF factor for tubular K-joint was also obtained. The numerical parametric study of the K-joint (using the finite element program) was described and its results were compared with experimental results. The stress effects of various parameters including α, β, γ, τ and θ on the stress in the K-joint were investigated. The stress distribution for each parameter was introduced. The study showed that the maximum stress of the joint varied according to the variation of joint parameters.
基金co-supported by the International Cooperation of RFBR-NSFC (No. 51111120088)the financial support from the National Natural Science Foundation of China (No. 50975014)
文摘To obtain the influence of fluid pressure and temperature on warm hydroforming of 5A06-O aluminum alloy sheet, the unified mechanics equilibrium equations, which take through- thickness normal stress and friction into account, were established in spherical coordinate system. The distribution of through-thickness normal stress in the thickness direction was determined. The relation between through-thickness normal stress and fluid pressure was also analyzed in different regions of cylindrical cup. Based on the method of subtracting one increasing function from another, the constitutive equation of 5A06-O applied to warm hydroforming was established and in a good agreement with uniaxial tensile data. Based on whether the thickness variation was taken into account, two mechanic models were established to do the comparative study. The results for the studied case show that the calculated stress values are pretty close according to the two models and consistent with results of finite element analysis; the thickness distribution in flange computed by the second model conforms to the experimental data. Finally, the influences of fluid pressure on the flange thickness and radial stress were analyzed.
